Geodemographic data resources, contd.
However, the tabular detail of the aggregations is specified by the generating agency solely for its own purposes and often contains either limited, useless or no information regarding the phenomenon that the geodemographer wishes to investigate, describe or model, although the scope of data items is immense (many thousands of tabular cells).

Small area census data are provided primarily in "raw" form. That is, simply as counts of the entities in the universe being tabulated for a given geographic area such as persons, families, housing units or households (occupied housing units) .

In fact, the acquisition, translation, preprocessing, retrieval, reduction, validation, imputational editing of suppressed or missing data, transformation, updating and projection or interpolation of secondary aggregate data is usually the largest part of the effort in geodemographic analysis. At this time, professional consultants and/or private 'value-added' data firms do much of this work, sparing the end user problems and pitfalls that might totally discourage the undertaking of a geodemographic analysis.

 The following diagram, Figure 1., illustrates the primary dimensions of the public data systems in the United States which produce and disseminate secondary or "public" data. They are time (frequency of publication), space (size of geographic aggregate) and volume (number of items of information and amount of tabular detail in the data).


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